"The limited role of a Court reviewing the exercise
of an administrative discretion must constantly be
borne in mind. It is not the function of the
court to substitute its own decision for that of
the administrator by exercising a discretion which
the legislature has vested in the administrator.
Its role is to set limits on the exercise of that
discretion, and a decision made within those
boundaries cannot be impugned: Wednesbury
Corporation.
It follows that, in the absence of any statutory
indication of the weight to be given to various
considerations, it is generally for the
decision-maker and not the court to determine the
appropriate weight to be given to the matters
which are required to be taken into account in
exercising the statutory power...I say "generally"
because both the principle and authority indicate
that in some circumstances a court may set aside
an administrative decision which has failed to
give adequate weight to a relevant factor of great
importance, or has given excessive weight to a
relevant fact of no great importance. The
preferred ground on which this is done, however,
is not the failure to take into account relevant
considerations or the taking into account of
irrelevant considerations, but that the decision
is "manifestly unreasonable". This ground of
review was considered by Lord Greene M.R. in
Wednesbury Corporation, in which his Lordship said
that it would only be made out if it were shown
that the decision was so unreasonable that no
reasonable person could have come to it. This
ground is now expressed in ss.5(2)(g) and 6(2)(g)
of the AD(JR) Act in these terms. The test
has been embraced in both Australia and
England...However, in its application, there has
been considerable diversity in the readiness with
which courts have found the test to be satisfied:
cf., e.g., Wednesbury Corporation and Parramatta
City Council, with the conclusions reached in
South Oxfordshire District Council v. Secretary of
State for the Environment; Shoreham-By-Sea Urban
District Council; and Minister of Housing and
Local Government v. Hartnell. But guidance may be
found in the close analogy between judicial review
of administrative action and appellate review of a
judicial discretion. In the context of the
latter, it has been held that an appellate court
may review a discretionary judgment that has
failed to give proper weight to a particular
matter, but it will be slow to do so because a
mere preference for a different result will not
suffice: Lovell v. Lovell; Gronow v. Gronow;
Mallet v. Mallet. So too in the context of
administrative law, the court should proceed with
caution when reviewing an administrative decision
on the ground that it does not give proper weight
to relevant factors, lest it exceed its
supervisory role by reviewing the decision on its
merits."